The present invention relates to a screw member for fastening a plurality of members to be fastened, and more particularly, relates to a technique for preventing the fastening of the members from becoming loose.
In order to fasten a plurality of members to be fastened, screw members such as bolts and nuts are often used, and in order to prevent the fastened screw members from becoming loose, a locking member such as a spring washer is normally used.
In order to prevent the screw members fastened to each other from becoming loose, without using such an additional part, there has been used a self-lock screw member as described in the Japanese Patent Publication No. 56-19492 and the Japanese Patent Publication No. 3-46686.
The self-lock screw member described in the Japanese Patent Publication No. 56-19492 is constructed such that a flank angle of a screw thread of a first screw member is set to be smaller than a flank angle of a screw thread of a second screw member meshed therewith, and in the thread of the first screw member, there is formed a slit radially extending from the point thereof. This screw member is formed such that when the first screw member and the second screw member are thread-connected, the thread of the first screw member elastically deforms in the direction that the slit becomes narrow, and due to a righting moment thereof, the self-lock function is exhibited.
However, in this self-lock screw member, an intersecting angle formed by a thread flank of the first screw member and the top portion of the screw thread is relatively small. Accordingly, in a case where the first and second screw members are thread-connected the thread point of the first screw member may sink into the flank of the second screw member, or the point may elastically deform before the screw thread of the first screw member elastically deforms.
In this connection, with the self-lock screw member as described in the Japanese Patent Publication No. 3-46686, the thread flank of the first screw member is constituted of a pair of first slopes forming from the base portion of the thread to the middle portion of the thread; and a pair of second slopes forming from the middle portion of the thread to the point, wherein an intersecting angle with the first slope is an obtuse angle. Also, a flank angle formed by the pair of first slopes is set to be smaller than that of the thread of the second screw member meshed therewith, and a flank angle formed by the pair of second slopes is set to be larger than a flank angle formed by the pair of first slopes.
Accordingly, when the first screw member and the second screw member are thread-connected, the thread of the first screw member comes in contact with the thread of the second screw member in an intersecting portion of the first slope and the second slope, that is, in an obtuse-angled portion. As a result, there is no possibility that a part of the thread of the first screw member sinks into the flank of the second screw member, nor the contact portion elastically deforms.
With the self-lock screw member as described in the Japanese Patent Publication No. 3-46686, however, since the thread of the first screw member is constituted of two surfaces, the contact area between the thread of the first screw member and the thread of the second screw member at the time of thread connection is reduced, compared to the case of the self-lock screw member as described in the Japanese Patent Publication No. 56-19492. Therefore, there is a problem in that a fastening power and a relative strength of the first screw member and the second screw member decrease.
It is an object of the present invention to improve a fastening power and a relative strength in thread connection of screw members having a loosening prevention function.
A screw member of the present invention is a screw member, comprising a first screw member having a screw body and a screw thread formed by helically protruding from said screw body, said screw thread having two thread flanks and formed with a notch groove at a top portion of said screw thread; a second screw member which is thread-connected with said first screw member by a relative rotation about a center of an axis; a first crest portion formed around said top portion of said screw thread, having a first inner surface extending into said notch groove of said screw thread and having a first flank continuous to one of said thread flanks; a second crest portion formed around said top portion of said screw thread, having a second inner surface extending into said notch groove facing said first inner surface via said notch groove, and having a second flank continuous to the other of said thread flanks; said first flank and said second flank of said first and second crest portions being provided to form an intersecting angle to be set smaller than a flank angle formed by said two thread flanks; and said respective crest portions being provided to elastically deform so as to approach to each other when said first screw member is thread-connected with said second screw member, to thereby apply a fastening power to said second screw member.
According to the present invention, the thread-connected two screw members exhibits a loosening prevention effect due to elastic deformation of the first crest portion and the second crest portion, while bringing the entire thread flank from the base portion to the point into contact with the other screw member on the both flanks of the screw thread. As a result, a strong fastening power can be obtained, and a clamping force applied to the screw thread is distributed over the thread, thereby enabling improvement in the relative strength in thread connection.
A screw member of the present invention is a screw member, comprising: a first screw member having a screw body and a screw thread formed by helically protruding from said screw body, said screw thread having two thread flanks and formed with a notch groove at a top portion of said screw thread; a second screw member which is thread-connected with said first screw member by a relative rotation about a center of an axis; a first crest portion formed around said top portion of said screw thread, having a first inner surface extending into said notch groove of said screw thread and having a first flank continuous to one of said thread flanks; a second crest portion formed around said top portion of said screw thread, having a second inner surface extending into said notch groove facing said first inner surface via said notch groove, and having a second flank continuous to the other of said thread flanks; said first flank and said second flank of said first and second crest portions being provided to form an intersecting angle to be set smaller than a flank angle formed by said two thread flanks; and said respective crest portions being provided to bite into said second screw member when said first screw member is thread-connected with said second screw member.
According to the present invention, since the both crest portions formed on the first screw member bite into the second screw member while cutting the second screw member, the contact area between the both screw members increases, and the first screw member serves as a tapping screw, thereby enabling reliable prevention of loosening.
A screw member according to the present invention may be such that the first screw member is a bolt and the second screw member is a nut, or the first screw member is a nut and the second screw member is a bolt.